This was not happening to doors downstairs (where almost all cement had been removed). For a time I was mystified about this and later inclined to think it solely due to insufficient vapour extraction from the upstairs bathrooms. I now think the lack of internal breathability of any of the upstairs walls must have been at least partly the issue. Although it wasn't a driver of the decision to remove the concrete when that decision was taken, I hope and expect this issue will not recur in future now the upstairs walls are breathing.
Fast forward to March.... out goes all the bedroom furniture to be stacked in a covered pile in the sitting room and in comes protective hardboards for the flooring (fingers crossed - they're still in place at time of writing) and the kango hammers. The ensuing mess and cloud of dust was in some respects the hardest of the several phases I've experienced with this rolling project. There was no sanctuary this time. Visiting involved airbnbing in the locality.
|At one stage it was literally crawling between rubble and scaffold bars to get upstairs|
|One of the 2 previously covered fireplaces plus the original back window from before the addition of the mid C19th annex|
|The mid C19th annex upstairs with the other rediscovered fireplace|
While the destruction phase was going on my main job was to decide on the lime plaster to go onto the walls. Needless to say, I (over)analysed the options and probably tried the patience of Kevin and Pat in the process. The suggestion had been to use Secil Ecocork which is a significantly breathable lime plaster system from Portugal which has some insulating properties in addition to its breathability. This product seems to have achieved a broad degree of acceptance within the community working with lime in Ireland in recent years. It is frequently used on stone walls with what seems a good track record to date.
A couple of months earlier, at the same time as the work on the attic, it was used in two small areas downstairs which I asked Pat and Kevin to work on as an 'experimental canvass' - a porch area out of which I was moving a boiler and the dank and windowless small toilet in the north east corner of the house. I had been satisfied with the results to date.
|External walls of porch plastered with Secil Ecocork plaster system|
On the other hand, the plastering job to come upstairs would probably be the largest order for internal plaster I would make ever and I wanted to try and make sure it was fully thought through. Do it once and try not to have regrets later!
I struggled a little because there is a whole world of internal lime plasters and it can be confusing for the uninitiated to find their bearings. I researched online, sent a question out to a LinkedIn building conservation group, asked Pete Ward and gradually concluded there were 2 broad options:
1) hydraulic lime mortars (plasters which set faster and harder giving more strength but as a tradeoff are somewhat less porous depending on the natural hydraulic lime 'NHL' strength of the makeup)
2) non hydraulic, 'fat' or 'soft' lime plasters (which have a much slower set and give you a softer-looking plaster with maximum breathability)
The hydraulic lime mortars, because of their strength, are used for almost all outdoor lime rendering and had been used by Kevin and Pat in 2014 on the external lime rendering of my house (an NHL 3.5 mix in that case). They are also often used for internal plastering and the Secil Ecocork is is a pre-mixed hydraulic lime plaster system - this is arguably part of its success in terms of uniformity of resulting performance and lower risk in application.
For me, if I was going to undergo all the destruction of removing cement, then I wanted to replacement lime plaster to have maximum breathability - why settle for less? The reason why you might settle for a little less breathability is that hydraulic lime plasters with added aggregate (for example cork) can have slightly higher insulating characteristics than a soft lime plaster. As far as I could glean, strength of plaster and/or insulating properties come at the expense of ultra-breathability.
Given this trade-off, Pete Ward's observation that the thermal mass of 2ft-plus thick solid walls constitutes your real insulation was the cardinal point to bear in mind. One of the other contributors on the linkedin conservation group put it nicely: 'the (thermal) specification of a few mm of inner wall covering is not going to make much difference one way or another. Re vapour permeability - go for the most porous, as the walls should be able to act as moisture reservoirs - dependent on environmental conditions'
Once I had that direction, the decision became easier; I considered asking Kevin and Pat to add lime putty to the Secil Ecocork system to take it down from NHL3.5 (I believe, although its hard to tell from the product literature) down to something like a very breathable NHL2. In the end though, given I wasn't under any time pressure and could take time for plaster to set, I opted for the ultra-traditional choice for internal plaster on these islands; soft lime hemp plaster.
Soft lime hemp takes patience in application and then in waiting before it can be painted. To give an idea, the application of coats started in the second week of April and Kevin and Pat were still being cautious about painting one section of plaster on a shaded east facing wall late in June.
Time and performance (i.e. breathability) will be the test of the success or otherwise of this plaster choice. The initial result however, from an aesthetic viewpoint (I write this as the furniture begins to go back into the bedrooms) is very pleasing - a plaster with an soft-edged organic look and feel to it.
|Final coat beginning to dry in May|
|Fat lime plaster can give pleasing organic shape to corners|
Next post: a nasty surprise uncovered ...